1. Field of the Invention
The present invention relates to an image processing apparatus, control method, and a computer-readable medium storing a program. Particularly, the present invention relates to image reduction processing.
2. Description of the Related Art
Recently, efforts are being made to decrease the print count by using N-up printing and the like for resource saving. However, when rendering data is reduced in N-up printing, thin horizontal lines may disappear as shown in FIG. 1A. Various methods have been proposed to thin out bitmap data for reduction, but suffer poor quality (BLACKONWHITE (for binary data), WHITEONBLACK (for binary data), COLORONCOLOR (for multilevel data), and HALFTONE (for multilevel data)). These methods have many restrictions such that their main targets are binary data, and smoothing must be applied simultaneously for multilevel data. For example, text bitmap data is created in accordance with the resolution without considering reduction, so shape is lost upon reduction. There is an effective means for binary data which reflects information by ORing data at the two ends of a line to be thinned out. However, this is not effective for multilevel data because ORing different colors makes the color unclear. A reduction method effective for binary and multilevel data is to reduce vector data of the outline of rendering data. In this method, vector data is reduced by transform processing of multiplying it by a transform matrix. There is also proposed a method of determining the thinning order by paying attention to horizontal and vertical line elements (see Japanese Patent Laid-Open No. 4-93892).
However, simple transform processing reduces a 1-pixel wide horizontal line or the like to have a line width of smaller than 1 pixel, and such a thin line may not be rendered after quantization (FIG. 1B). Also, a line slightly inclined from a horizontal or vertical line, italicized text, and the like cannot be appropriately processed using the method of determining the thinning order by paying attention to horizontal and vertical line elements, like Japanese Patent Laid-Open No. 4-93892.